Cardiac electrophysiology (EP) studies that are used to diagnose and treat heart arrhythmia are conducted using catheters in minimally invasive medical procedures. Specifically, the studies involve the placement of a catheter through a patient's blood vessels to reach the heart for testing and treatment of the heart. Catheters are medical devices in the form of hollow flexible tubes for insertion into a part of the body usually to permit the passage of fluids or keep open a passageway. A catheter is normally accompanied with accessory components such as a control handle, catheter tips, surgical tools, etc., depending upon the application (and thus as a whole may be referred to, more properly, as a catheter system).
In minimally invasive medical procedures, catheters are often used to deliver therapy in such a way that requires a respective catheter tip to be in contact with the tissue being treated. Radio frequency ablation (RFA) is one example of such a procedure, wherein the therapy is carried out with an ablation catheter having a tip that delivers high frequency alternating current so as to cause heating of the tissue. In the case of an RFA procedure to carry out treatment during an EP study, electrodes on a catheter tip are used to ablate specific sections of, for example, the pulmonary veins. The goal is to have the RFA heat the tissue to the point of causing lesions that will block certain electrical pathways in the heart tissue that are contributing to the arrhythmia.
RFA procedures and other minimally invasive medical procedures are routinely performed under image guidance. For example, bi-plane and monoplane x-ray fluoroscopy (fluoro) images are typically used to give the physician or health professional valuable real-time feedback during a respective procedure. FIG. 1a shows a typical real-time fluoro image used in an EP study with two electrode catheters 2, 4 inserted into the heart of a patient. The darker shaded region 6 in the middle of the image shows the contour of the heart. While image guidance systems and techniques can provide visualization of the catheter tip, and sometimes localization of the tip within some coordinate space, the challenge is often in relating that tip information to the actual location of the anatomy of interest. Sometimes this might be accomplished by using optimal imaging planes that clearly show both the anatomy and the device, although this can be difficult in a complex anatomy such as the heart. In the case of the heart, this is further complicated by the heart beating motion, patient breathing motion and catheter motion. A lasso catheter 8, shown in FIG. 1a, can be placed on, for example, the pulmonary vein to assist in guidance during a procedure. However, this catheter 8 is not always available during different types of clinical procedures.
Other techniques involve the use of pre-acquired volumetric imaging data or 3D models of the anatomy superimposed with the real-time imaging. Recently, a EP-Suite software package from Siemens was introduced that allows for multi-modal preoperational (pre-op) 3D images of the patient to be annotated and overlaid upon the live fluoro images (acquired, for example, from either computed tomography (CT) or magnetic resonance (MR) imaging modalities). These images can help physicians and other health professionals better locate the correct region to ablate. A necessary portion of the workflow is the requirement to manually align a previously created mesh of, for example, the heart in the pre-op 3D image to the fluoro images. Automation of this registration step would result in a faster and simplified workflow.
The automatic registration of the heart or other structures of the body, to fluoro data, however, can be very challenging due to the low contrast of most tissues in fluoro images and possibly the missing-angle projection geometry (e.g., bi-plane geometry) used in clinical settings. Currently, there is no automatic method available to 1) correct the patient's setup error between the pre-op 3D image (e.g., CT or MR image) and the ob-board fluoroscopy or 2) track the intra-treatment heart, for example, position under respiratory motion. Moreover, registrations between pre-op MR images and fluoroscopic images present additional difficulties due to the substantial imaging gap between two different modalities (MR and X-ray). For example, when generating DRRs (Digitally Reconstructed Radiographs) from an MR image to perform a registration with the fluoro images, there is no density information available to allow the generation of a realistic X-ray image.
FIG. 1b shows an example of a substantial initial set-up error between a pre-op 3D image and the real-time fluoroscopy image of FIG. 1a. The overlay image 10 is a DRR generated from the segmented heart volume of a pre-op MR image. The shading of the overlay 10 shows the depth of the heart along the plane's normal direction.
Thus, there is a need to improve image guidance systems and techniques for visualization and localization of catheters and other tools/objects relative to the anatomy of interest of a patient during medical procedures.